2 results
Redox interactions of technetium with iron-bearing minerals
- J. M. McBeth, J. R. Lloyd, G. T. W. Law, F. R. Livens, I. T. Burke, K. Morris
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- Journal:
- Mineralogical Magazine / Volume 75 / Issue 4 / August 2011
- Published online by Cambridge University Press:
- 05 July 2018, pp. 2419-2430
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- Article
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Iron minerals influence the environmental redox behaviour and mobility of metals including the long-lived radionuclide technetium. Technetium is highly mobile in its oxidized form pertechnetate (Tc(VII)O4–), however, when it is reduced to Tc(IV) it immobilizes readily via precipitation or sorption. In low concentration tracer experiments, and in higher concentration XAS experiments, pertechnetate was added to samples of biogenic and abiotically synthesized Fe(II)-bearing minerals (bio-magnetite, bio-vivianite, bio-siderite and an abiotically precipitated Fe(II) gel). Each mineral scavenged different quantities of Tc(VII) from solution with essentially complete removal in Fe(II)-gel and bio-magnetite systems and with 84±4% removal onto bio-siderite and 68±5% removal onto bio-vivianite over 45 days. In select, higher concentration, Tc XAS experiments, XANES spectra showed reductive precipitation to Tc(IV) in all samples. Furthermore, EXAFS spectra for bio-siderite, bio-vivianite and Fe(II)-gel showed that Tc(IV) was present as short range ordered hydrous Tc(IV)O2-like phases in the minerals and for some systems suggested possible incorporation in an octahedral coordination environment. Low concentration reoxidation experiments with air-, and in the case of the Fe(II) gel, nitrate-oxidation of the Tc(IV)-labelled samples resulted in only partial remobilization of Tc. Upon exposure to air, the Tc bound to the Fe-minerals was resistant to oxidative remobilization with a maximum of ∼15% Tc remobilized in the bio-vivianite system after 45 days of air exposure. Nitrate mediated oxidation of Fe(II)-gel inoculated with a stable consortium of nitrate-reducing, Fe(II)-oxidizing bacteria showed only 3.8±0.4% remobilization of reduced Tc(IV), again highlighting the recalcitrance of Tc(IV) to oxidative remobilization in Fe-bearing systems. The resultant XANES spectra of the reoxidized minerals showed Tc(IV)-like spectra in the reoxidized Fe-phases. Overall, this study highlights the role that Fe-bearing biogenic mineral phases have in controlling reductive scavenging of Tc(VII) to hydrous TcO2-like phases onto a range of Fe(II)-bearing minerals. In addition, it suggests that on reoxidation of these phases, Fe-bound Tc(IV) may be octahedrally coordinated and is largely recalcitrant to reoxidation over medium-term timescales. This has implications when considering remediation approaches and in predictions of the long-term fate of Tc in the nuclear legacy.
Psychosocial and illness related predictors of consultation rates in primary care – a cohort study
- N. KAPUR, I. HUNT, M. LUNT, J. McBETH, F. CREED, G. MACFARLANE
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- Journal:
- Psychological Medicine / Volume 34 / Issue 4 / May 2004
- Published online by Cambridge University Press:
- 21 April 2004, pp. 719-728
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Background. Despite extensive research, the reasons why patients consult their doctors are unclear. The aim of the current study was to identify the psychosocial and illness related factors that independently predicted primary care consultation over a 5-year period.
Method. We carried out a prospective, population-based cohort study with three waves of data collection by postal questionnaire in one general practice in Greater Manchester (UK). Consultation data were sought from primary care records on a random subsample of 800 adult patients. The main outcome measure was the number of consultations (including surgery and home visits) over the 5 years of the study as determined by raters blind to questionnaire responses. Questionnaire measures included the 12-item version of the General Health Questionnaire, the Illness Attitude Scales, a somatic symptom scale, a fatigue scale, a functional assessment of disability.
Results. Consultation data were obtained on 738 patients (92% of selected subjects), who accounted for 12182 consultations. Negative illness attitudes, the presence of physical and psychiatric disorder, health anxiety, changes in psychological distress, reported physical symptoms and demographic factors such as age and sex were independently associated with consultation over a 5-year period. These variables together accounted for a difference of ten consultations per year between groups.
Conclusion. Consultation in primary care is a complex behaviour with a complex aetiology. Terms such as ‘frequent attenders’ may be less helpful than recognizing a number of dimensions that operate across the whole spectrum of consultation frequency. Future research should consider the wider context of consultation.